Tungsten finds many different applications useful for the fabrication of nano-devices. Deposition of pure tungsten may be used to fill the holes that make contact to the transistor source and drain (“contact holes”) and also to fill vias between successive layers of metal. This approach is known as a “tungsten plug” process. The usage of tungsten may be developed due to the good properties of the films deposited using WF6. However, it is necessary to provide an adhesion/barrier layer, such as Ti/TiN, to protect the underlying Si from attack by fluorine and to ensure adhesion of tungsten to the silicon dioxide.
Tungsten-silicide may be used on top of polysilicon gates to increase conductivity of the gate line and thus increase transistor speed. This approach is popular in DRAM fabrication, where the gate is also the word line for the circuit. WF6 and SiH4 may be used, but dichlorosilane (SiCl2H2) is more commonly employed as the silicon source, since it allows higher deposition temperatures and thus results in lower fluorine concentration in the deposited film.
Tungsten nitride (WNx) is considered to be a good barrier against diffusion of copper in microelectronics circuits. WNx may also be used in electrodes for thin-film capacitors and field-effect transistor.
Molybdenum oxide may be used as a thin layer for DRAM capacitors. See, e.g., US2012/309162 or US2014/187015 to Elpida. The molybdenum oxide layer may be deposited on a TiN layer before deposition of a ZrO2 layer. The molybdenum oxide layer may then help increase the deposition rate of the ZrO2 layer. The molybdenum oxide layer may be deposited on the ZrO2 layer and a TiN layer deposited on the molybdenum oxide layer producing a TiN/MoOx/ZrO2/MoOx/TiN stack. The molybdenum oxide layers in the stack may reduce leakage current.
Electrochromic devices are optoelectrochemical systems that change their optical properties, essentially their transmittance, when a voltage is applied. As a result, the optoelectrochemical systems may be used in many applications, such as, but not limited to, smart windows, sunroofs, shades, visors or rear view mirrors, flat panel displays for automotive, architectural, display, and optoelectrical applications like skylights, panel displays, aquariums, light filters and screens for light pipes and other optoelectrical devices. Transition metal oxides have been used as inorganic electrochromic materials. Among those transition metal oxides, tungsten trioxide, WO3, an n-type semiconductor, is one of the most extensively studied materials due to its electrochromic properties in the visible and infrared region, high coloration efficiency, and relatively low price. The color of WO3 changes from transparent or yellow to deep blue when it is reduced under cathodic polarization.
Organic Light Emitting Diode (OLED) devices involve emission of light at a specific wavelength range when a voltage is applied. The use of transition metal oxides as the electrode interface modification layer at anode and cathode in OLEDs has also been reported for reducing the operational voltage, one of the main parameter to improve device reliability. Among those transition metal oxides, tungsten oxide or molybdenum oxide as an anode buffer layer offers advantages such as very high transparent in the visible region and energy level matching with organic molecules. (Applied Physics Letters, 2007, 91, 113506).
JP07-292079 discloses metathesis catalyst precursors having the formula M(Y)(OR2)x(R3)y(X)zLs, wherein M is Mo or W; Y is ═O or ═NR′; R1, R2, and R3 is alkyl, cycloalkyl, cycloalkenyl, polycycloalkyl, polycycloalkenyl, haloalkyl, haloaralkyl, (un)substituted aralkyl, arom. groups containing Si; X=halogen; L=Lewis base; s=0 or 1; x+y+z=4; and y≥1. The catalyst precursor is synthesized from M(Y)(OR2)4, such as W(═O)(OCH2tBu)4.
Chisholm et al. disclose preparation and characterization of oxo alkoxides of molybdenum. Inorganic Chemistry (1984) 23(8) 1021-37.
WO2014/143410 to Kinestral Technologies Inc. discloses multi-layer electrochromic structures comprising an anodic electrochromic layer comprising lithium, nickel, and a Group 6 metal selected from Mo, W, and combinations thereof. Abstract. Para 0107 discloses that the source (starting) material for the Group 6 metal may be (RO)4MO.
David Baxter et al. Chemical Communications (1996), (10), 1129-1130 describes the use of different tungsten(VI) oxo alkoxides and tungsten(VI) oxo alkoxide β-diketonate complexes that are volatile precursors for low-pressure CVD of tungsten oxide electrochromic films. However, the molecules may be solid, difficult to purify effectively, or costly to prepare due to relatively high number of synthesis steps.
WO99/23865 to Sustainable Technologies Australia Ltd. discloses that synthesis of tungsten (VI) oxo-tetra-alkoxide [WO(OR)4] from WOCl4, alcohol and ammonia produces an insoluble tungsten-containing compound. WO99/23865 discloses that excess ammonia can be added to dissolve the precipitated tungsten compound, but that the final tungsten oxide obtained is unsuitable as a film for electrochromic applications.
M. Basato et al. Chemical Vapor Deposition (2001), 7(5), 219-224 also describes the use of W(═O)(OtBu)4 by self-evaporation, in combination with H2O, to form WO3 material at 100-150 C.
J. M. Bell et al. describe the preparation of tungsten oxide film for electrochromic devices using W(═O)(OnBu)4 (Solar Energy Materials and Solar Cells, 2001, 68, 239).
Dmitry V. Peryshkov and Richard R. Schrock describe the preparation of W(═O)(OtBu)4 from W(═O)Cl4 and Li(OtBu). Organometallics 2012, 31, 7278-7286.
Parkin et al. disclose CVD of Functional Coatings on Glass in Chapter 10 of Chemical Vapour Deposition: Precursors, Processes and Applications. Section 10.4.3 discloses that several tungsten alkoxides, oxo alkoxides, and aryl oxides have been investigated, such as WO(OR)4, wherein R=Me, Et, iPr, and Bu. Parkin et al. note that these precursors provide a single source precursor, with no need for a second oxygen precursor. Parkin et al. note that these precursors suffer from low volatility.
U.S. Pat. No. 7,560,581B2 discloses the use of the bis-alkylimido bis-dialkylamino tungsten precursors for the production of tungsten nitride in ALD mode with or without plasma for copper barrier diffusion applications.
Miikkulainen et al. disclose ALD deposition using Mo(NR)2(NR′2)2 precursors. Chem Mater. (2007), 19, 263-269; Chem. Vap. Deposition (2008) 14, 71-77. Chiu et al. disclose CVD deposition of MoN using Mo(NtBu)2(NHtBu)2. J. Mat. Res. 9 (7), 1994, 1622-1624.
A need remains for developing novel, liquid or low melting point (<50° C.), highly thermally stable, Group 6 precursor molecules suitable for vapor phase thin film deposition with controlled thickness and composition at high temperature.